Centrifugal separators are well known for separating fluids of different densities or for separating particulate matter from liquids. The principle of operation of such a centrifugal separator is that a housing contains a rotor which is supported therein to spin at high speed about a substantially vertical axis. Fluid from which contaminants are to be removed is supplied to the rotor at elevated pressure along the axis of rotation. As this fluid passes through the rotor, denser contaminant materials or particles are separated therefrom centrifugally and retained in the rotor, typically as a cake adhering to the interior surface of the rotor, which is cleaned or replaced at intervals.
Self powered centrifugal separators in which the fluid from which contaminants are to be removed also provides the drive for the rotor have long been used in lubrication systems of vehicles, as well as in other industry of separation processes. GB 2160796 and GB 2296942 disclose self-powered centrifugal separators of the type which comprises a base, a substantially vertical spindle upstanding from the base, a rotor mounted on the spindle for rotation thereabout by reaction to fluid emission from rotor nozzles, the base having an inlet passage for said fluid and the spindle having an axial bore and outlets therefrom to supply fluid to the rotor from said inlet passage, and a cover mounted on the base and enclosing the rotor. In this type of separator the fluid is supplied at pressure from the base of the housing and flows upwards through the axial bore to outlets near the top of the bore, which is typically a blind bore. A releasable cap is typically mounted at the top of the spindle to secure the cover.
Hitherto it has not been possible to use a centrifugal separator, whether of the self powered type or when powered independently of the fluid being filtered, To clean, i.e. remove contaminant particles from, a liquid where the contaminant particles are abrasive, for example honing oil, grinding machine coolant, electrode discharge machining fluid, or oil quench fluid from furnaces. This is because the bearings upon which the rotor is mounted become very rapidly worn by the action of the abrasive particles and needed to be replaced too frequently. For example, after as little as 30 seconds operation with liquids containing abrasive particles the bearings may be worn sufficiently to prevent or at least adversely affect balanced rotation of the rotor and continued efficient centrifugal separation, and need to be replaced.
Also, it has not hitherto been possible to use such a separator (filter) to remove contaminant particles from a liquid which is not itself a lubricant as the liquid typically acts as lubricating fluid for the rotor bearings, as well as drive fluid for the rotor in the case of a self powered separator. Thus, it has not been feasible to use such a filter for water purification purposes, for example, for removal of particles from the water.